Re: CR Block copies, always 6 in

From: K Gopalakrishnan <>
Date: Mon, 24 Mar 2008 21:10:17 -0700
Message-ID: <>


This is just a soft limit. You can infinitely create cloned buffers in your buffer cache and we don't limit that. This limit is enforced only  under certain conditions and memory pressure is one among them. Check my other post for some more detials.


On Sun, Mar 23, 2008 at 5:10 PM, amonte <> wrote:
> Hi all
> I read from somewhere, I think the wait interface book where it states that
> the number of clone copies of data block is governed by _DB_BLOCK_MAX_CR_DBA
> which is set to 6. If there will be more than 6 copies then Oracle will wait
> for the buffer, this is what I dont get, wait?
> So I fired up 7 sessions and see what kind of wait is this! I updated the
> same table (EMP from scott tiger), 14 rows in same data block and each
> session updates a row, then each session fires a query agaisnt EMP. I
> noticed that the number of CR is never more than 6 despite having 7 updates
> concurrently and I dont see what is really going on. Does this mean whenever
> the 7th CR block is being cloned one of 6 previous CR is being overwritten
> or "destroyed"?
> I did the test in
> Alex

Best Regards,
K Gopalakrishnan
Co-Author: Oracle Wait Interface, Oracle Press 2004

Author: Oracle Database 10g RAC Handbook, Oracle Press 2006
Received on Mon Mar 24 2008 - 23:10:17 CDT

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